For years, his name was best-known as the answer to a popular quiz question. “Who was the only British Field-Marshal to have served at every rank of the Army?” Today, it is hardly known at all, even for that. Because it does not follow that this conferred any special distinction on him.

Robertson was promoted Chief-of-Staff (professional head of the army) in 1915, having never led men into action in his life. His limited schooling showed-up embarrassingly, forcing his colleagues to cover for him. His coarse manners and deliberate rudeness ruffled many feathers. To his perceived discredit, he was a supporter of Haig, and largely responsible for Passchendale and the Somme. But he had attracted royal favour; the King was impressed by his long climb from the barrack-room. And by chance, as commander of the Army of Occupation in Cologne in 1919, he played tennis with a young infantry officer who pleaded with him to add his name to the next Staff College intake, the only path to high rank. He was a Captain Montgomery.

It must be said that this memoir is of its time. There is such a thing as perishable data, and much of the detail would have carried far more interest on the publication of this book in 1921 than it would today. The drill for conferences with non-English speaking generals… How to merge part of the Training Directorate with the Directorate of Home Defence… What to do with a whole lot of mules that had been left in western Egypt… Such issues could hardly hold the attention now.

Robertson does reveal an odd thing about cavalry rank at the turn of the century. It was actually more common for a Troop Sergeant-Major to be recommended for a commission than his equivalent in the infantry (CSM). But the cavalryman was more likely to have to turn down the honour because of the lavish entertainment that would be expected of him - except in India, where the cost was a lot more manageable. And when it was Robertson’s turn, his unit was indeed just off to India. But money would remain a problem almost to the end; even as a Field-Marshal, he was often on half-pay.

As for the title of the book, it should strictly have been ‘From Trooper to Field-Marshal’, but that wouldn’t sound so neat. I think we can forgive Sir William for never having served as a private, and put it down to semantics. And perhaps a few readers may yet be stirred by the determination of a young man from nowhere who looked up at the peaks, and said “Why not?”